The present invention relates generally to motion sensing devices, and more particularly to micro-machined gyro sensors for measuring an applied angular velocity.
The advent of micro-machining has opened the way for a re-assessment of older traditional solutions to problems and has created opportunities to create improved implementations of established principles with integrated interface and control electronics in a highly developed system. One example is the implementation of a gyro in an integrated circuit with silicon circuitry.
Gyros have been effectively used in aircraft and other navigational systems with great effect as angular motion sensors, but at high cost. Implementing a gyro in integrated form can lead to a cost reduction which makes their use more feasible in the automotive field for such uses as navigation, stability control, suspension control and general vehicle dynamics management.
Generally, a gyro is a mass that is excited to rotate or oscillate or vibrate in a stable manner. The inertia of the mass resists attempts to disturb the motion. Moving the mass so as to change the relative position of the plane in which it is moving causes a reaction, known as the Coriolis effect, that leads to an acceleration at right angles to the plane of the motion. This acceleration is the result of, and proportional to, the perturbing motion. By measuring the acceleration in the orthogonal direction(s), a value for the perturbing velocity can be determined.
The problems associated with gyros are well understood and at the traditional macro level have generally been addressed and overcome. These solutions however do not have direct equivalents in the micro-machined environment where the cost-benefits of integrated manufacture come from silicon processing techniques developed for high volume processing of integrated circuits. These processing techniques are not suitable for implementing the individual machining requirements or mechanical adjustments needed for micro-machined gyros. The minute mechanical adjustments that are made on parts, which in the macro situation are quite large, would be proportionally small on the micro level and consequently more difficult and costly to implement.
In addition to the basic mechanical problems of producing a balanced mass that can be set up to oscillate or spin to act as a gyro in a micro-machined environment, techniques are needed to supply energy to the mass to excite its motion, and to measure the orthogonal acceleration(s) caused by the perturbing velocity. A major problem also exists where the mass exhibits a tendency to oscillate off-axis, known as quadrature deflection, or to oscillate in more than one mode. A well-known problem exists, for example, where an oscillating mass, in addition to the basic linear motion, oscillates in a twisting or rotational manner. Such unwanted oscillations occur when the mass is not perfectly balanced or aligned. These unwanted oscillations act as if they were externally applied velocities which cause additional Coriolis accelerations that must be detected and separated from the wanted accelerations.
Accordingly, there is a need in the art for a system and method for determined and compensating for the effects of unwanted imbalances in gyros in an efficient, cost-effective manner so as to provide for a more accurate determination of an imposed velocity.
The present invention provides for such a gyro by embodying in the design additional elements to enable the oscillation of the mass to be set up in either of two or more different modes. The effects of the unwanted imbalances are determined and compensating signals applied to cancel the unwanted effects thus enabling more accurate determination of an imposed velocity.
According to the invention, a gyro sensor includes an oscillating mass supported on a number of flexible beams micro-machined into an integrated circuit device, such as a silicon CMOS device. Several Piezo-electric elements,deposited onto the beams, are provided to excite the mass and to measure the accelerations. Integrated in the device are electronic circuitry that initiates and maintains the oscillation and electronic circuitry that detects and measures the subsequent motion. Additional circuitry is also provided to determine the effects of any quadrature oscillation that may be present due to manufacturing imperfections and to generate signals to drive the oscillating mass in such a manner as to eliminate or reduce such unwanted motion. Eliminating or reducing such unwanted motions facilitates determining the Coriolis acceleration, and thus the magnitude of an external perturbing velocity.
According to an aspect of the invention, a micro-machined gyro sensor capable of measuring an externally imposed velocity is provided which typically comprises a mass coupled to a rigid annular support by a first pair of opposing flexible members and a second pair of opposing flexible members, wherein the first pair of members define a first axis, and wherein the second pair of members define a second axis substantially orthogonal to the first axis. The gyro sensor also typically includes a first pair of driving elements deposited on the first pair of members, a second pair of driving elements deposited on the second pair of members, a first pair of sensing element deposited on the first pair of members, and a second pair of sensing element deposited on the second pair of members. The first sensing elements generate first signals proportional to the oscillation of the mass along the first axis, and the second sensing element generate second signals proportional to the oscillation of the mass along the second axis. The second pair of driving elements on the second pair of members is used to correct any off-axis oscillation along the second axis such as that due to mechanical imperfection. The gyro sensor also typically includes a control circuit coupled to the first and second pairs of driving elements, wherein the control circuit generates a control signal which when applied to the first pair of driving elements causes the mass to oscillate along the first axis, and a detection circuit coupled to the first and second sensing elements, wherein the detection circuit receives the first and second signals and generates an output signal having a component proportional to the imposed angular velocity and a second component proportional to the unwanted off-axis oscillations along the second axis. In one embodiment, a second signal is applied to the second pair of driving elements by the control circuit such as to reduce or eliminate the unwanted oscillations.
According to another aspect of the invention, a micro-machined gyro sensor capable of measuring an externally imposed velocity is provided which typically comprises a mass coupled to a rigid annular support by a first pair of opposing flexible members and a second pair of opposing flexible members, wherein the first pair of members define a first axis, and wherein the second pair of members define a second axis substantially orthogonal to the first axis. The gyro sensor also typically includes driving means coupled to the first pair of members for causing the mass to oscillate perpendicular to the plane of the rigid annulus and detection means, coupled to one of the first pair of members and one of the second pair of members, for detecting and comparing oscillations of the mass along the first axis and along the second axis so as to measure the (Coriolis) acceleration caused by the imposed velocity and to determine a signal to be applied to the driving means to reduce or eliminate any off-axis or other unwanted oscillations.
Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.